Furfural, benzoin condensation

Furfural undergoes condensation to furoin under the catal3rtic influence of cyanide ions in aqueous alcohol solution (compare Benzoin, Section IV,125) ... 

Tetra-n-butylammonium cyanide is a better catalyst for benzoin condensation reactions than is sodium cyanide, and >70% yields are obtained under mild conditions [63, 64] tetra-ethylammonium cyanide is less effective. Polymer-supported ammonium catalysts have also been used to promote the benzoin reaction and, although yields are only moderate (40-60%), the convenience of removal of the catalyst is an advantage. Use of chiral ammonium groups produces an enantiomeric excess of chiral products from the condensation of benzaldehyde, but furfural tends to produce a racemate [65]. 

The acyloin (benzoin) condensation is applicable, not merely to benzaldehyde itself, but also to its homologs, to its alkoxy derivatives, and to furfur-aldehyde. It fails, however, with free hydroxybenzaldehydes and with halo-genated nitro and amino benzaldehydes and cinnamaldehyde gives diminutive yields. 

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